Mass spectrometry is being employed as a structural and analytical aid in investigations of the antibiotics dermostatin, candimycin, berninamycin, scopafungin, hamycin, antiamoebin, aureofungin, vacidin A, and aminocyclitol antibiotics, as well as of soybean phytoalexin, and comple mixtures of compounds from marine organisms. Mass spectrometry, using stable isotopes, is also being applied to studies of the biosyntheses of the antibiotics neomycins B and C, chloramphenicol, nybomycin, the streptovaricins, and geldanamycin, as well as to biosyntheses of the parasympathomimetic fungal metabolite slaframine. Field desorption and field ionization mass spectrometry are under study, employing high resolution as well as gas chromatographic techniques.